text:
How does the use of Leading Edge Root Extension help in increasing stall angle?
Leading Edge Root Extensions were first used in Northrop F-5A/B Freedom Fighter, which first flew in 1959. After that, many fighter air-crafts have used it, some of which are mentioned after the question. The reason behind using such extension is delay of stall at very high angles of attack. How does the use of Leading Edge Root Extension help in increasing stall angle?
Northrop F-5A/B Freedom Fighter

author unknown, public domain (source)
Sukhoi Su-27

photo by Dmitriy Pichugin, GFDL 1.2 (source)
McDonnell Douglas F/A-18 Hornet

photo by LCPL John McGarity, USMC, public domain (source)

Can you possibly provide attribution for the images (source)?

The idea is to generate a vortex near the fuselage. In most cases we do not want any vortexes, as the unnecessary air movement always causes an increase in drag. In this case however, you need them.
As the air flow separates from this small triangle wing while at large angles of attack, it gains a rotary motion (if you look at the left wing standing in front of the aircraft it will rotate clock-wise). This vortex inducts further swirling movement across the wing.
Now, if you are familiar with fluid dynamics, you can imagine that this will decrease air pressure at the top of the wing (not much impact on the bottom side), which is what we want - higher lift is generated.
What is more important in this the case, is the boundary layer. If you provide it with energy, making it more turbulent, it will pay off with sticking to the wing surface even while flying at large angles of attack. Obviously the larger is the angle without stall, the higher lift can be generated. Therefore an airplane with wing extensions can perform sick maneuvers like cobra and other more useful in aerial combat. Of course it requires a huge amount of spare thrust, but you do not have to worry about that in military jets.

In addition to this reply, would like to point out that the leading edge is now well forward of the engine inlet. Airflow will tend to come straight into the inlet even when the aircraft itself is at a high angle of attack, leading to less engine air starvation. (Specifically thinking of the F/A 18).

The inlet flow alignment as mentioned by @ALANWARD is a relevant topic to include in the answer directly.

@DamalaniSingh: I wonder why you see the need for a bounty when web pages such as this give a good explanation already. In order to avoid a link-only answer, I will summarize the LEX-related gist here (LEX = leading edge extension).
You may know that a delta wing forms a powerful vortex on its suction side at high angle of attack which allows it to work well past angles of attack where conventional wings with less leading edge sweep have stalled. Adding what is in essence a small delta ahead of the main wing will give you the benefit of both: Better L/D and overall more lift at low angle of attack, plus much improved high-alfa capabilities.
The mechanism is the same as for regular delta wings, but the vortex will do its magic not only on the LEX, but also on most of the wing behind it. First a picture of CFD simulations, taken from the Aerospaceweb page mentioned above:

Now proof that the same happens in the real world, again copied from the Aerospaceweb page:

Note the wool tufts on the LEX and wing: The flow over the wing is really separated, because the tufts point in all directions except backwards. What is also visible is the disadvantage at high angle of attack: The vortex bursts behind the wing, which causes extreme vibrational loads on the tail fins. They needed to be reinforced at their root to extend the structural life of the airframe. Again, also the last picture of this answer is copied from the Aerospaceweb article. You should read it yourself!

@VictorJuliet: And lastly, please give the bounty to Pawel! His answer was first, and it is correct. I have enough reputation already.

DamalaniSingh: I wonder why you see the need for a bounty Damalani is one of a set of accounts suspended for voting irregularities, the bounty is probably to find a way around the system.

No worries about the bounty, I got more rep points from upvotes than the bounty itself. Anyway I have enough rep to move around the forum freely ;]

The wing leading edge extension (LEX) creates almost no lift at Mach < 1, since the air flows from bottom to top through its leading edge. In case of Mach > 1 however, the LEX comes into operation. It creates, per unit area, mind, almost the same lifting force as the rest of the wing. As a result, the LEX prevents the aerodynamic center from shifting backwards to some extent. The "ogival" delta wing (used on Concorde) works in this respect in much the same way as the wing with LEX does. To sum up, it all has to do with flying and maneuvering quantities, not pure aerodynamics.
Sources (in Russian):

https://www.migavia.com/books/mednikov2.html
http://www.avialibrary.com/component/option,com_mtree/task,viewlink/link_id,289/Itemid,3/
https://mishaengineer.ucoz.net/load/uchebnaja_literatura/aehrodinamika/mednikov_v_n_dinamika_poleta_i_pilotirovanie_samoletov_1976/4-1-0-3

Pages 41, 42, Fig. 2.14.

This answer is inconsistent with the other answers posted. Can you point (link) to sources which confirm your explanation?


text:
Why did the Concorde require a droop nose and how did it work?
As seen in the picture below, Concorde used to have a droop nose which would be deployed during takeoff/landing and would be retracted to the normal position while in cruise (do reduce drag).
Concorde with a droop Nose deployed

Concorde in normal configuration

According to the wiki page on Concorde, this Droop Nose was added in the later versions of Concorde when the authorities raised questions about the restricted view which was available to pilots during landing/take off at very high angles of attack (which was required for the Concorde).

What are the other possible solutions which could have been employed instead of the droop nose to tackle to the restricted view from the cockpit?
Why did Concorde had to land and take off at higher than normal angle of attacks?
How did the Droop nose actually work? (Which mechanism was used to deploy and retract it)

You may look at those videos to see it in action.

What are the other possible solutions bordering on too broad, but let's see what the others say.

1) Though already mentioned that this might be too broad, I would dare to guess a properly fitted camera could do the trick. But I doubt that this would be effective considering the technology of the era that Concorde was developed.
2) Concorde due to its design for supersonic speeds, it was generating too little lift at low speeds (like those needed for landing). So they had to take into advantage another way of producing lift: vortex lift. In order to produce vortex lift, you need relatively high angles of attack and consequently high pitch attitude.
3) I cannot answer this since I am not an engineer. Though with little googling I found this. It seems to be very detailed, with photos of the lever and diagrams of the mechanism.

Not quite an answer but an interesting side note: the pilots did train to land with the nose up in case it failed in flight. But actually Concorde had a "wonderful" autoland system and therefore under most circumstances it could land itself. Source: http://omegataupodcast.net/2015/02/166-flying-the-concorde/

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text:
Must I log aircraft checkout flights as dual received?
14 CFR 61.51 says:

(h) Logging training time.
  (1) A person may log training time when that person receives training from an authorized instructor in an aircraft, flight simulator, or flight training device.
  (2) The training time must be logged in a logbook and must:
    (i) Be endorsed in a legible manner by the authorized instructor; and
    (ii) Include a description of the training given, the length of the training lesson, and the authorized instructor's signature, certificate number, and certificate expiration date.

If I am rated in the aircraft and just getting a local FBOs checkout or familiarization flight with their instructor, must I (also) log it as dual received? Yes I see the word "may" in (h)(1)

Long story short, maybe. The FAA doesn't define "dual time" so it depends how you define it for your own purposes, but in practice most people use it to mean "training time". There's no definition of "dual" or "dual time" in 14 CFR part 1 or 61 and part 61 never mentions it, apart from a couple of references to "dual instruction". "Dual" is also not used in form 8710.
But "training received" is clearly defined, and 61.51 says you should log time in general if you need it to satisfy certification or currency requirements:

(a) Training time and aeronautical experience. Each person must
  document and record the following time in a manner acceptable to the
  Administrator:
(1) Training and aeronautical experience used to meet the requirements
  for a certificate, rating, or flight review of this part.
(2) The aeronautical experience required for meeting the recent flight
  experience requirements of this part.

So in your example, do you need to log the time for a) certification/currency purposes, and/or b) as training received? And if you do log it, is it "dual"?
For certification/currency, it's usually best to log everything: even if you don't need to show the FAA something, your insurance company or FBO might ask you for details of your flying time.
As for training, in order for a flight to be "training received", the instructor has to endorse your logbook:

(2) The training time must be logged in a logbook and must:   (i) Be
  endorsed in a legible manner by the authorized instructor; and   (ii)
  Include a description of the training given, the length of the
  training lesson, and the authorized instructor's signature,
  certificate number, and certificate expiration date.

That's a simpler case: if the instructor didn't sign your logbook then you didn't receive training.
But let's say that you decide to log the flight for one or both of the reasons above. Is it "dual"? Well, since there's no official definition of "dual" then it depends what you use it to mean.
Again, practically speaking, most people use "dual" to mean "training": my logging software uses it that way, and many paper logbooks seem to as well. So I only log dual if I have a corresponding endorsement from my instructor. (The software also has options like "instructor on board" or "introductory flight" that I can use for the scenarios you described.)
As a specific example, I did an FBO checkout ride in a new aircraft type a few months ago. I was already rated for the aircraft category/class and the instructor with me didn't endorse my logbook, he just updated the FBO's internal documentation to state that I'm now allowed to rent it. So I logged the time as PIC, but not dual.

so, to be clear, I no longer need any dual unless I want an ATP (unlikely) or to add a  rating (yo, Instrument-Rotocraft!)

@rbp Yes, you don't need to log anything unless it's for additional ratings or currency. But personally I don't see any downside to logging everything. If you fly your own, 'self-insured' aircraft VFR only, never carry passengers and are completely sure that you will never add a new rating then in theory you only need to log flight reviews, but most people need to track passenger currency (day and night), instrument currency, FBO requirements, insurance requirements etc. as applicable. It just seems easier to log everything.

the downside is that I have 6 ratings, 4 endorsements, and checkouts in 40-something aircraft. That's a lot of dual, and I don't want to look like I have had a CFI in the right seat everytime I fly.

As the student you are not required to log training time (because (h)(1) says may and not must). In fact you are not required to log time at all unless you're documenting that time for purposes under 61.51(a) (experience/training required for a rating, a flight review, or for "currency" purposes).
There is no reason not to log the time as "dual received" however, and if your FBO's insurance requires you to receive a checkout/instructional flight prior to renting that logbook entry is your proof that you received that instruction from them.
If you are rated for the aircraft in question you may also log the time as Pilot In Command, unless there are other circumstances precluding that (a common one is again insurance requirements).

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text:
Can an airplane on an SVFR clearance land when visibility is less than 1 mile?
Let's say I'm on an SVFR clearance and the flight and reported ground visibility deteriorates less than 1 mile, what happens?

If the pilot is on an SVFR clearance, the weather inside the surface area deteriorates below 1 mile visibility, and the pilot has the airport in sight, he can inform the controller that he has the field in sight and will be cleared to land. The pilot is responsible for continuing to the airport or exiting the surface area in order to remain visual.

NOTE− Clear an aircraft to land at an airport with an operating
  control tower, traffic permitting, if the pilot reports the airport in
  sight. The pilot is responsible to continue to the airport or exit the
  surface area. 14 CFR Section 91.157 prohibits VFR aircraft (other than
  helicopters) from landing at any airport within a surface area when
  flight visibility is less than 1 mile. A pilot could inadvertently
  encounter conditions that are below SVFR minimums after entering a
  surface area due to rapidly changing weather. The pilot is best suited
  to determine the action to be taken since pilots operating under SVFR
  between sunrise and sunset are not required to be instrument rated,
  and the possibility exists that flight visibility may not be the same
  as ground visibility. 14 CFR Section 91.3 authorizes a pilot
  encountering an inflight emergency requiring immediate action to
  deviate from any rule of 14 CFR Part 91 to the extent required to meet
  that emergency. Flight into adverse weather conditions may require the
  pilot to execute the emergency authority granted in 14 CFR Section
  91.3 and continue inbound to land. Air Traffic Control Handbook, 7−5−4

And if you are instrument rated and current, you can get a popup  instrument clearance.

Did you just answer your own question? Confused

@Kamran it's allowed and encouraged, it helps SE become a good reference for questions like that.

@ratchetfreak Got it, I haven't been here long. I need to get to grips with the rules! I can think of a few questions now! I'm glad you cleared this up!

@casey in these circumstances, you can't get a pop-up. the only place you can get a pop-up in the surface area is on the ground. If you're in the air in the surface area with viz less than 1sm, and you call up the tower and ask them for a pop-up, they will tell you to "maintain VFR" (while they call Approach to coordinate), which you already know you can't do. Even if you can get a clearance, they will ask you if you can provide your own terrain and obstacle clearance while you climb to the MIA or MEA, which you know you also can't do. maybe you can try to fly a DP if you can find the runway:)


text:
What is the difference between targeted airspeed and selected airspeed?
Are Targeted Airspeed and selected Airspeed the same thing?
And can someone explain in what cases managed airspeed or pilot selected airspeed would be used, i.e. for different flight phases/situations etc.?

This article some useful information.

Please provide some context to the question. Where did you encounter these terms? Aircraft operations, cockpit interface design, autopilot control law design, flight deck based interval management?  The answer really depends on the context in this case.

These terms obviously stem from an Airbus flight deck.
Anything selected represents pilot's discretion. If you want to keep a certain speed, HDG or altitude, you would pull the corresponding FCU (Flight Control Unit = Autopilot Panel) knob. This means in Airbus philosophy: I have control.
Anything managed represents a flight management calculation. If you want to fly, e.g. in the most economic way, you push the corresponding FCU knob and therewith "handover the controls to the aircraft".
The calculations for managed autopilot options are derived from e.g. gross weight entries on the INIT page or current gross weight, Angle of Attack, Air Data Computers, Cost Index, ... depending on the flight phase.
So, you always prefer to follow the economically calculated way and use managed modes. Whenever ATC requests you to keep a certain speed, sink/climb rate, heading whatever, you pull the knobs and select the target values.

V-Target (should be a subscript Target) is the speed you're going to maintain flying down final in the landing configuration.  Your selected airspeed is where you have the cursor right now, so as you go from cruise at say .78 mach to a descent at 280 knots to the descent below 10,000' at 250 knots, to slowing in the pattern to 200 or 210 knots, then configuring with various flap settings, your selected speed changes to each of those, until you've extended the last increment of flaps, and you "set Target" in the window (so that's where your speed cursor goes on the airspeed indicator or tape), and now the Target speed is your selected speed as you fly down final.
You might simplify that explanation to, Target is what you WILL set to fly the final approach in landing configuration, while your Selected speed is what you have selected right now.


text:
Can a Cessna 162 Skycatcher be flown IFR in IMC?
This question is similar to these questions:

Are there any LSA aircraft that can be flown IFR in IMC?
What are the FAA requirements for an aircraft to be IFR certified?

Unfortunately I couldn't find a definite answer to the following question:
If a private pilot is instrument-rated, can he/she file an IFR flight plan and fly IFR in IMC in a Cessna 162 (Skycatcher), assuming the C162 is equipped with the optional autopilot? (is it really a requirement to have a functioning autopilot for IFR in IMC?)
As far as I know, the Skycatcher has all the required equipment for IFR, including a "real" Continental engine (unlike most other LSA's using Rotax engines)

Which regulations are you interested in? FAA, EASA or something else?

AFAIK, there are no C162 aircraft registered outside the U.S. But I'm asking about the U.S. (FAA)

There's no requirement for an autopilot to legally fly IFR in IMC.

@FredLarson You're right. I thought I read that somewhere but that was about RVSM, not IFR in general.

The Skycatcher GPS is not IFR approved, and the plane does not have any NavRadios (so no VORs, NDBs, ILS) But the GPS system does not have any Approach Procedures in it, and I don't believe they can be loaded.  So you'd be left flying GPS-only approaches with paper plates, and no vertical guidance.

Not in the US. The C162's POH says:

The Model 162 Skycatcher is not equipped or certified for IFR flight

That means that under 14 CFR 91.9 it may not be operated IFR. But, FAA Order 8900.1 allows an exception for aircraft not certified for IFR to be operated under IFR in VMC only:

A.    IFR Training in Visual Meteorological Conditions (VMC). Instrument flight training may be conducted during VMC in any aircraft
  that meets the equipment requirements of part 91, §§ 91.109, 91.205,
  and, for an airplane operated in controlled airspace under the IFR
  system, §§ 91.411 and 91.413. An aircraft may be operated on an IFR
  flight plan under IFR in VMC, provided the PIC is properly
  certificated to operate the aircraft under IFR. However, if the
  aircraft is not approved for IFR operations under its type
  certificate, or if the appropriate instruments and equipment are not
  installed or are not operative, operations in Instrument
  Meteorological Conditions (IMC) are prohibited. The PIC of such an
  aircraft must cancel the IFR flight plan in use and avoid flight into
  IMC.

An autopilot isn't required for IFR flight in the US (see 14 CFR 91.205(d)) and the question you linked. I didn't check the full equipment list to see which required instruments are missing from the C162, but even with full IFR equipment if it isn't certified for IFR then it can't be operated in IMC per the regulations above.

Note that "gyros" do not have to be spinning-mass gyroscopes: Both laser gyros and MEMS systems have been certified by the FAA. (The folks at Crossbow wrote a great paper on the hoops they had to jump through which is an interesting read.)

This raises the question about what the controller will think when you cancel IFR in Class B because of weather. Or does he already know from the type identifier that you're not certified for IFR flight, and that you will cancel if the weather deteriorates.

The section title is "IFR Training...", but the plain text suggests that an IFR pilot can fly the plane, for non-training purposes, in the IFR system, just because they choose to, and not for training.

@rbp Interesting scenario (worth a question?). ATC knows the equipment code, I guess /U would be correct for a C162 (or /I?). But that's just for navigation purposes, it doesn't mean that the flight can legally or practically operate in IMC.

There's a corollary question of, say, a Mooney which is type certified for IFR, but may not be IFR current, flying under Order 8900.1.

The 162 is approved for day/night/VFR flight only, though it can serve for IFR training in VFR conditions, it cannot be flown in IMC


text:
Is this WWI movie scene realistic?
In a poignant scene of 1933 WWI film The Eagle and the Hawk (not to be confused with the same-name 1950 western film), while the pilot played by Fredric March performs a loop-the-loop in his – I believe – Airco DH.9 (is that correct?) to evade a German opponent, his observer/gunner falls out of his place and plunges to the ground (he had already been hit and probably killed by the German, but the pilot wasn't aware of it, so this is a real trauma for him).
See the scene here, starting from about 57:25.
Besides the dramatic value of this scene within the narrative, would such a fall as the gunner's be realistic? If those aircraft were capable of such manoeuvres, wouldn't the crew be somehow secured?

The plummeting observer casts a vast shadow across the landscape - it's like watching Gulliver fall onto Lilliput.

A loop is about 3G on the initial pull, declining to maybe half a G over the top, then increasing to 3G on the pull out.  If you go in at the proper entry speed etc and you want to make it reasonably round.  If you release enough back pressure to go even slightly negative over the top, whatever is unsecured falls out (as well as all the crap on the floor coming up into your face, and, if carbureted, the engine quitting momentarily).   All it would take is a little push on the stick while rounding the stop, for whatever reason.
Observers weren't strapped in because they had to be free to move around to do their thing.
So that scene is perfectly plausible.

And in addition, the op's statement that the aircraft would maintain 1 G throughout betrays a misunderstanding or misconception of the physics involved. An wings level aircraft at one G will not change it's pitch attitude. The force of gravity and the Lift on the wings are equal at one G, so the nose position or flight path angle will not change.  To increase it you must pull back on the stick and increase Lift, (thereby increasing the Load-Factor (G) to something greater than 1G).

Thanks, @CharlesBretana, I have amended the text of the question.

@DaG, not to be nit-picky, but the statement "at least 1 G" is still wrong. It should be " at least -1 G", as the answer by John K states. At the top of the loop the total G on the aircraft is, (as it always is) the vector sum of the aircraft G plus "God's" G, and as long as this vector sum remains pointed down, the aircraft will continue in a circle. The only way the aircraft might not continue turning towards the earth at the top of a loop is if the pilot pushes forward on the stick to establish -1 or greater negative G.

It should just be "positive G", meaning centrifugal force still acting toward the floor of the aircraft .  At the top of a loop you are normally less than 1, but need to stay more than 0.  You will get quite close to zero G if you have to, to maintain a rounded top.  You ease off the back pressure over the top in a way that gives a constant pitch rate (or you try to) as the inverted horizon is coming through and you may ease off to nearly 0G, or ballistic, in doing this but you have to careful to not quite go that far.

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text:
I just want to fly, so where do I go
Ever since I was 10, I've always wanted to pilot an airplane by myself. I don't want to do it for the money I really just want live that "dream of flight" but where I grew up in a society that doesn't favor "dreams" or even flight. I really want to know, isn't there a place I could go and just fly without having to pay anything. To be honest, the fees at flight schools are really outrageous and discouraging. I want to know if there is a place in this world that I can just live that dream. By the way, sitting in passenger plane crowded with a bunch of people for several hours doesn't count at all. Please I hope that someone can help me.

May I ask how old you are? In Germany it's possible to learn gliding at the age of 14. That could be a first step. Sometimes the education is free for teenagers. Well, not totally free. You have to compensate with doing things on the ground, like operating the winch or something. I don't know the situation in other countries.

There are programs like this https://www.eaa.org/en/eaa/aviation-education-and-resources/eaa-youth-education/eaa-young-eagles-program that give free introductory rides to young people, but really there isn't a place where you can learn to fly for free.  (Other than enlisting in the military and being accepted into pilot training, but I wouldn't call that 'free'.)  Airplanes cost money, as does fuel and the instructor's time.  Those flight school fees may seem outrageous when you're the one paying them, but AFAIK most schools are not making big profits.

Very little is free, especially time in expensive aircraft. I don't think this is on topic but if it's deemed to be on topic it's impossible to answer without information on your age/location.

In the US, join an EAA chapter, go to meetings. Make friends with a pilot (or three) and mention to one that you've always wanted to go but can't afford it. One of them will probably offer to go up with you. Depending on your age, you can also join the Young Eagles which does free flights for  youth.

If you join the military, dedicate years of your life to service, work hard, show skill and talent, and are lucky enough to be selected, they will train you to be a pilot and fly for free.  You will even earn a modest salary at it.
In the USA, the Army has more pilots than any other branch.
The Air Force, Navy, Marines and Coast Guard all have flight programs as well.

It is better for obvious reasons to get your pilot's license before joining the military for lots of reasons but I guess this could technically work.

Yeah, but a PPL will generally cost a minimum of $8K.  The criteria in the question was "isn't there a place I could go and just fly without having to pay anything."

@William: Is it actually an advantage to have a PPL before enlisting, assuming you want to go for pilot training?  I'd always understood that the (US - the only one I know much about) military preferred to do its own training.

@jamesqf your seniority is determined by the number of flight hours I'm pretty sure.  That is how it worked when my grandfather served.  If you start flying at 13 you are sure to have more flight hours better ranking maybe I would assume so.

I wouldn't say there is anywhere specific you can go that allows this. For what its worth no one is going to throw you the keys to their plane and let you take it for a spin. Not only is that pretty much illegal in most places, but its outright dangerous for you and everyone beneath you. There are however a few things you can do.
Most flight schools in the USA (and presumably elsewhere although I cant speak for anything outside the US) offer "Introduction Flights" to just about anyone who shows up. Depending on where you go these cost about $100 USD these days and you will get anywhere from 30-60 minutes of time in the pilots seat. They often will let you do just about everything from takeoff to right before landing. Keep in mind their will be an instructor in the right seat giving you directions.
The internet is full of airplane owners and reaching out on some forums may yield you a flight in your local area (depending on where you live). This can often be had for the price of buying the pilot lunch, or if your lucky for free.
Here in the US the Civil Air Patrol has a youth program. I see the kids at my local field go up every once in a while and as far as I know its free.
It may help if you edit the question to identify your location.


text:
Why were there passengers allowed on Concorde's route proving flights?
Based on this site, Concorde needed to fly 750 hours to prove its airworthiness and be used in regular service. Air France and British Airways flew two Concords (F-BTSC and G-BOAC respectively) on a total of 254 flights, with... 11180 passengers combined! How come there were passengers allowed to be on the plane when it was doing flights to get its airworthiness certificate?

Don't forget that if the aircraft hadn't been "safe to fly," the crew (who unlike the passengers can make a professional informed judgement about safety) wouldn't have flown it. You don't magically survive an accident better than someone else just because you wear a fancy uniform and they don't!

Southwest Airlines is currently conducting similar tests with the 737 MAX with employees and media flying on board. You might find this video informative.

@alephzero I don't know, man. Their uniforms are really quite fancy indeed.

Bear in mind that these tests weren't to prove the safety of the aircraft per se, just to show that it would work as an airliner. It had to be loaded up with an appropriate complement of passengers and luggage to prove this.
However proving flights may not generate revenue from passengers - they are either selected through an application process or chosen at random, and take part in the proceedings free of charge.
CAA AIRWORTHINESS INSPECTOR‘S HANDBOOK (Page 2, point 3)

I was just wondering, in the Concorde case, was it a random lottery held for marketing reasons (how good would that be!), or "friends of the family", or ??

@JoeBlow on a few of the very early test flights, the Minister of Technology (one Tony Benn, of all people) managed to get himself invited along - according to Francis Spufford, whose essay on Concord is worth reading, he was utterly starstruck and always brought a camera. He later arranged a flight - one of the later tests before the proving flights proper - for BAC union shop stewards and their wives. I assume they didn't haul the factory staff along when they went to Singapore, though!

Amazing stuff !!!


text:
What are the structural differences between short- and long-haul airplanes?
As I understand it, pressurization cycles introduce the most stress on an airframe so maintenance intervals are tied to it. However, not all planes are equal in that regard, a long haul flight in a 747 might easily take 10 hours counting for one pressurization cycle while a 737 can do 6 trips in that time. Are short-haul planes build "sturdier" in this regard than their long-haul counterparts so that they are able to better cope with the amount of stress? And/or do they have to go into maintenance more often?

It also differs by operator.  Operator A can own a 734 which flies 6 legs per day on only short haul flights.  Operator B might own another 734 which flies mid-haul and only 2 legs per day.

Short haul planes are generally narrow-bodies which are naturally sturdier than wide-bodies, just because they're more compact and have less potential for flex

Yes, short range airliners are designed for up to 90.000 cycles whereas long range airliners can be designed for 40.000 cycles or less. And it is not only the pressurized cabin that needs to be designed for more load cycles, also the landing gear has a lot more work to do. This should become clear when you calculate how many miles/kilometers an airplane will taxi in its life and compare that to the design life of a regular car.
Your average short range airliner will easily taxi 5 times more miles in its life than your average car will drive.

I never thought about the taxiing, that's really impressive!

I must have missed this question the first time 'round. Peter, can you give some examples/calculations for the taxi distances. Many cars, in the US at least, will drive well over 100k miles (~160k kilometers), and I'm having a hard time grasping that a plane will taxi that distance. Fly? Certainly, but taxi?  Maybe I should make this a whole new question.

@FreeMan: Assume 1500m for both the take-off and the landing run, add taxi distance to and from the terminal, and on a big airport this will add up to 8 or 10 km of taxi distance per cycle. Times 90,000 makes three quarters to  a million km in taxi distance. If one airport on a leg is smaller (5 km taxi), the total is still almost 600,000 km.

Thanks, @PeterKämpf. I guess I never really thought about how far a plane really taxis. It does add up quickly. I guess part of it is that an airframe will usually be used for 30 years or so, but most cars are disposed of after 10-15.

90.000? That would be 5 cycle a day for 50 years without interruption !

@Antzi: Look how many cycles Ryanair is squeezing out of their 737s!.

Average to 5 ;)

Closer to 6, actually. However, they don't use planes for 50 years.


text:
Is the UK still part of the ECAA since Brexit?
Is the UK still part of the ECAA (European Common Aviation Area) since Brexit?
For instance is it possible for a Spanish Air Operator Certificate (AOC) holder to operate a scheduled commercial flight from the UK to Greece?

No, it is not still part of the ECAA. The EU and UK made a new agreement for Brexit, which you can read here. The part about aviation begins on page 534.
Under article 419, it states:

The Union shall enjoy the right for its air carriers to make stops in the territory of the United Kingdom to provide scheduled and non-scheduled air transport services between any points situated in the territory of the Union and any points situated in the territory of the United Kingdom (third and fourth freedom traffic rights).

So the specific situation you've asked about is legal, not because the UK is still part of the ECAA, but because the agreement between the EU and UK specifically provides for it.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What are the certification requirements for software used at airports?
If you develop software that is used at the airport and integrates into a departure control system (DCS), is it required to undergo some IATA certification processes?
When I search for IATA regulation on software used at airports, I can not find much. Actually I haven't found anything that states that, for example, a departure control system (DCS) must undergo some certification process.
I therefore ask, are there any certifications or validation requirements for software used at airports? For example if you develop a new DCS, would you be required to undergo IATA certification? What other hurdles (FAA, EASA, ...) are their for software used at airports?
Note, I explicitly want to exclude software that is used for air traffic control.

Do the existing DCS descriptions on vendor sites mention compliance to standards?

The short answer is yes, With larger airlines, they may own and manage their IT infrastructure at central hubs, so the airline will need to ensure their software works with their chosen peripherals. At smaller airports where this is not possible, many airports use a common use computer platform, managed by both the airport authority and commercial IT vendors. Ultra is one such example. Airline DCS software would need to undergo validation to ensure it will correctly interface with the various devices at the airport: bag tag, boarding pass, document printers, self-check-in kiosks, and gate scanners.
The Passenger and Airport Data Interchange Standards (PADIS) Board as well as the
Common Use Working Group (CUWG) provide direction to IATA for creating technical standards. CUPPS (Common Use Passenger Processing Systems), is the IATA standard recommended practice for such common use computer systems.
DCS systems also must be able to transmit advance passenger information to government agencies, for example TSA to verify the passenger is not on a terrorist watch lists. Requirements for transmitting such information is set by the UN EDIFACT PAXLST specification, but not all passenger information transmissions will be sent from a DCS system.
EASA and FAA are more focused on flight data (flight plans, ATC, and weather) and have specifications for receipt and transmission of that information, but the transmission is usually done by separate software.


text:
Why are aircraft of Russian origin not subject to frequent weighing and CG calculations like western aircraft?
Western miltary a/c maintenance requires routine weighing of the plane yearly or during major inspections.Whereas Russian miltary a/c maintenance does not insist on this kind of weighing,so much so that weighing is not part of any maintenance  schedule after initial manufacture ! Can some one give any plausible reason for this anomaly ?

it's a difference, but I hardly can see how it can be classified as anomaly.

Western doctrine is to keep all aircraft of one type in identical conditions. Once you change one thing, you do it for all aircraft of this type at the same time (or create a subtype). Routine weighing makes sure that the individual aircraft conforms to the type certificate.
Russian doctrine sees every airplane as an individual, and if something is changed, it needs to be documented, but not necessarily done on all other planes of that type. To every airplane belongs a (mostly) metal box with all documents, and they should tell you exactly what has been modified since it was produced. Weighing is now part of maintenance, but needs not be done if nothing has been modified.


text:
Who should handle an emergency when there's both a certificated pilot and a CFI on board?
While practicing for my commercial certificate in a T-tail Piper Arrow IV, I put the gear down on downwind, and one green light didn't come on.
In the right seat was a CFII/Multi, who had over 1,000 hours but less than 10 hours in Pipers, whereas I had about 300 hours, and over 200 in Pipers, having done my PPL in stiff-legged Cherokees.
As a certificated pilot, I was PIC, but we talked about how to handle the emergency, and the CFI and I decided that since I had so much more experience in Pipers, I would handle the emergency tasks, while he handled the radios and looked for traffic.
We did the proverbial tower fly by (although they wouldn't say anything except the gear "appeared to be down"), and they cleared me to land on any runway. Our landing was uneventful, and it turned out to be an electrical MX issue.
When we landed, however, the flight school nearly fired the CFI for not having taken control of the aircraft during the emergency.
Did we make the right decision for me to handle the emergency? Or should I have let the CFI/CFII/MEI with over 1,000 take over as PIC and handle the airplane?

Take over as PIC and handle the plane (= become PF) are completely separate things. Did they have problem with him not becoming PIC or him not becoming PF?

in VFR with a student rated in type, there is only one PIC, except for the usual exclusions, so I'm not sure what you mean

But there is no rule that PIC has to be the one who actually handles the controls. For training a rated student is PIC and PF, no other combination makes sense; but for the emergency you can change it. So you could have declared the instructor PIC and still split the tasks as you did. So I am asking whether they mind you didn't declare the instructor PIC, or whether they mind the task split.

Suffice it to say that the school wanted him flying the airplane and acting PIC, period,not some combination.  Furthermore, I think it would be a bad idea in this kind of situation to sit in the cockpit and hash out who is acting PIC and who is going to manipulate the controls. When we agreed that I would fly, there was no question who was acting PIC.

True, as long as you worked in agreement, it didn't really matter. And if you didn't, it would have been your decision as PIC up to that point.

What I think that many people are missing here (including the flight school, apparently) is that your instructor had much more experience and therefore out of everyone in the aircraft (who are the only people that matter at that point), he was the most qualified to decide how to proceed, and he decided that you should fly the aircraft.

You were PIC. It was your decision who would fly the aircraft and your decision whether to turn over PIC to him.

From a safety perspective both pilots should be handling any emergency that arises, each working to their individual strengths and expertise to ensure a safe outcome.
This is exactly what you did in the scenario you describe.
In terms of who calls the shots (acts as PIC for the emergency), generally the most qualified pilot onboard should be the one giving the orders. Deciding who that is falls to the pilots onboard (because they're the ones who will arrive at the scene of any resulting accident first).

So in my mind the question really is "How do I determine who is most qualified?" -- Any opinion we can give here comes dangerously close to second-guessing your emergency actions which is something I personally try to avoid, but I'm going to embellish your scenario above for illustrative purposes:

The Instructor
Former air force pilot ATP, CFI/CFII, MEI.
10,000 hours in various jets, 10 hours in an Arrow (doing this instructing gig.) and for the sake of argument no other time in PA-28s.
You
PPL + Instrument Rating, working on your Commercial.
300 hours, 200 in fixed-gear PA-28s and let's say 20 in Arrows.

I'll further assume you both kept your cool and didn't panic (because if either of you turned into a quivering blob that would automatically disqualify them from taking control of the aircraft).
If we go by the certificates, your instructor is certainly "more qualified" - and in 10,000 hours they've probably dealt with more real-world emergencies than you have.
If we go by "time in type" and experience flying PA-28 variants you're clearly more familiar with the general type, and possibly this specific aircraft & systems (like the emergency gear extension system).
Given the above, having you handle the controls seems to be the most logical course of action. The CFI can do "everything else" - communication, traffic scan, calling out checklists & altitudes, etc. - to ensure that you can concentrate on flying the plane and landing as safely as possible.

i know we're not supposed to say 'thanks' in the comments, but thanks for the part about not second guessing our decision-making

Is it usual to switch around the PIC role in flight (or even after an emergency has developed), absent anyone becoming quivering blobs? As a layman, I would have assumed the idea of having a concept of PIC in the first place would be not to have to waste time negotiating who should call the shots after a problem arises. If you depart with Guy A as PIC, but with the understanding that Guy B will take over if there's a problem, then is Guy A ever truly PIC for that flight?

@HenningMakholm I'm not sure about "usual", or if who is legally PIC would change (absent the quivering blob scenario) but the role of Pilot Flying can and occasionally does swap over (case in point, US Airways 1549: Sullenberger was PIC, Skiles was SIC and Pilot Flying for that leg, but after the bird strike Sullenberger took the controls).

@voretaq7: Yes, I'm aware that the PF role can (and routinely does) swap over. But unless I've misunderstood everything, that is distinct from the PIC role.

According to the FAA, if the student is rated and has the recency of experience, and the CFI is not acting as a required crewmenember (SIC or safety pilot), then the student can act as PIC, and the instructor is neither PIC nor a passenger. http://www.faa.gov/about/office_org/headquarters_offices/agc/pol_adjudication/agc200/interpretations/data/interps/2014/schaffner%20-%20%282014%29%20legal%20interpretation.pdf

Also see http://aviation.stackexchange.com/questions/6378/can-a-cfi-give-required-instruction-and-endorsements-on-a-3rd-class-medical

@rbp The student and instructor can agree beforehand that the instructor will be acting as PIC though - just because things should always be more complicated :)

True a prior agreement is a good idea, but it's also smart to make situationally aware decisions. Depending on the emergency, it may be smart to depart from the initial plan.

I don't see a mistake on the part of the CFI. After all, you were in the left seat and legally cleared to fly the aircraft, so it is up to you to decide. By clearly communicating and sharing the workload you did the right thing.
I guess the reason why the CFI got in trouble had more to do with insurance issues than with regulations. You don't mention it, but I assume the CFI was employed by the owner of the aircraft. It would be easier for the owner to settle with the insurance company if one of his employees is PIC in an emergency.

i updated the question to indicate that not only did he have CFI/CFII/MEI, but he also had over 1,000 and much more experience than me, and I rephrased the question a bit.

@rbp: I think this answer still applies and is best; it was your responsibility as pilot in command to decide how to handle the emergency, not of the instructor.

The instructor did the right thing by letting you fly.
I have 1200 hrs on the 737-300, 120 hrs 737-200, approx. 150 hours on the C172 and 80 hours approx Seneca (both a while ago), and a fATPL.
If I were in the Cockpit with somebody with more familiarity of the a/c characteristics I'd do Radio and assist as well, leaving them as PIC.
There is no time for an ego here.

Yes. As you specify it. This sounds perfectly correct.
To get the technicalities straight:
Who is PF? When you do your departure briefing, you specify who is PF. I was trained to start departure briefing with "I fly Piper Arrow, normal take-off. Maximum power, flaps 10, etc..." and then going on the emergency part, "...I will take all emergency actions, ..."
Who is PIC? This is answered by the column in which your enter the hours in your logbook.
As PIC, you are in command of the aircraft. You fly it or decide to hand over the flying duties.
The instructor can do everything else, checklists, watch your airspeed/altitude etc. However having many more hours than you he is aware of how to fly "an aircraft" better than you. So he can clearly detect if you are not going to be able to finish the job and should (if he feels the need) say "I have control".
Furthermore, even if the instructor had experience of landing with a wheel not locked, he may consider it good experience for you to land it anyway - provided you discussed how you were going to do it (airspeed, attitude, rudder (nose wheel), ailerons etc.)

most people don't enter the hours in their logbook before the flight. also the PF/PNF distinction doesn't hold for part 91 single pilot operations, unless the pilots at the controls are practicing CRM

As a CFI, whether I was giving instruction to a student pilot or in a jet, I would always give the same briefing concerning who would be in what role during an emergency.
The briefing would discuss numerous scenarios, but specifically address who will be the PF given their experience, recency, and time in type. This would always change from pilot to pilot and may change as the student gained time and experience. It's always a good idea to have a plan of action discussed well ahead of any departure.
A good example is the Miracle on the Hudson: Jeff Skilling was the PF and Sully was the PM when they departed. It was briefed that in the event of an emergency, Sully would handle the radios and fly the aircraft while Jeff would ran the emergency checklist, so as soon as they loss thrust Jeff transferred controls over to Sully and we all saw what happens when preparation and luck come together at a point in time.

I don't think luck applies. This was strictly preparation and experience. Sully treated the plane like a large heavy glider, which was a craft he had experience flying. Other than the lack of power he had a fully functional aircraft. He bled the airspeed off but didn't stall it. He hit the water at a very shallow angle while still having directional control of the aircraft. These are all skills that glider pilots have to develop. The passengers were not lucky either, they were fortunate.


text:
Is it ATC's responsibility to ensure read backs are correct?
I have experienced this a few times in the last couple of months. When the ATC assigns me a squawk code and I enter it in the transponder, a few minutes later when I try to reconfirm the squawk code, they give me a new code. I know that they can see me on the radar anyway, just may not identify me positively. I noticed this more on an inbound flight to a towered airport.
This happened yesterday too. I was assigned to squawk 6451. I replied to confirm it and entered it in the transponder. While holding short for takeoff, when I asked the controller to reconfirm the code, he said that it is 6455.
What is the controller's responsibility if they confirm an incorrect read back? Since this happened to me several times, I am concerned if such incident can impact safety, traffic advisories or aircraft separation?

Didn't your instructor teach you to write down your clearances?

Terrible handwriting + writing while flying = questionable results for squawk codes :-D sometimes I have to write without looking. On the ground everything is fine, but this has also happened on the ground and I wrote the wrong code down clearly, then read it back and was not corrected!

If you can't even bother to write 4 digits, you'll never be able to get an instrument rating. What would you do with this? “Cessna 12345 cleared to Nashville as filed, fly runway heading, climb and maintain three thousand, expect seven thousand one zero minutes after departure, departure frequency one two four point six five, squawk two seven one three.”

@rbp I agree and know I need to work on it :-) like I said on the ground is fine for me, it's while flying that gets me... Either way, my question was about the controller's responsibility to ensure correct read back if I clearly repeat it back wrong

I think the question is misplaced.  The responsibility of the controller is clearly stated in the AIM.  You are the PIC, however.  If you're asking who is responsible you shouldn't be flying a plane unless you're just doing research or asking the question for some other reason.

@user6035379 This was during my primary training and I haven't since had this problem, though in retrospect it is still very odd that they didn't catch this several times.

Yes a controller absolutely must listen to read-backs and ensure they are correct. This is commonly referred to as hear-backs.
Consider the following excerpt from ICAO Annex 11, Air Traffic Services (emphasis mine):

3.7.3    Read-back of clearances and safety-related information
3.7.3.1    The flight crew shall read back to the air traffic controller safety-related parts of ATC clearances and instructions which are transmitted by voice. The following items shall always be read back:
a) ATC route clearances;
b) clearances and instructions to enter, land on, take off from, hold short of, cross and backtrack on any runway; and
c) runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions and, whether issued  by the controller or contained in ATIS broadcasts, transition levels.
3.7.3.1.1    Other clearances or instructions, including conditional clearances, shall be read back or acknowledged in a manner to clearly indicate that they have been understood and will be complied with.
3.7.3.1.2    The controller shall listen to the read-back to ascertain that the clearance or instruction has been correctly acknowledged by the flight crew and shall take immediate action to correct any discrepancies revealed by the read-back.

If, after a read-back by a flight crew, the controller neither acknowledges nor corrects the read-back, most flight crews will percieve this as an implicit confirmation of the read-back. This makes hear-back errors very dangerous, and is the reason why the pilot-controller communication loop has, not two, but three steps, the third step being the hearback:

While your example of an incorrect transponder code is rather trivial, incorrect read-backs can be extremely dangerous. For instance, they could result in a level bust, mid-air collision or runway incursion.
Therefore, performing appropriate hear-backs is an essential part of ATC training, and is taught to ATC trainees from day one. The importance of active listening is demonstrated in a simulator environment, where simulator pilots will occasionally - either intentionally or by mistake - make incorrect readbacks, the result of which will be a dangerous situation, if not corrected promptly.

Further reading:
Pilot-Controller Communications
Read-back or Hear-back

A controller, should be on the lookout for all incorrect readbacks. But controllers are human, and can easily miss them, or say things in correctly. Incorrect squawk codes are often more of an annoyance versus an actual separation issue. It'd become an issue if they didn't take action when it was noticed that there was an incorrect code airborne, and let you truck on your way and not perform appropriate handoffs or inform others of any issues with your flightplan/target.
Most of the time, an incorrect beacon code will be flashing on the scope, if it's not assigned to someone else, and the controller will look through their list to find the correct code. If you tag up under someone else's code, then it becomes more of an issue, as they have to realize it's incorrect, suspend the datablock, and flightplan(or most likely drop it out of the system and reenter it) (flightplan issue is often delegated to others in the operation), and hunt for your correct code.


text:
How do big planes like 737 manage fresh air for passengers during flight?
How do the big planes (e.g. A380 or 737) flying on high altitudes manage to get fresh air for passengers and crew during the flight?
I know the inner space of the plane used for passengers and crew is sealed and the pressure is maintained within some range.
However in standard flight altitude of about 10-14 km there is not enough oxygen to breathe.  I am not sure whether the standard oxygen ratio is still about 21% and you only have less air (lower pressure).
We talked two possible solutions and maybe I am still wrong:

using some pumps and small pressure tanks to suck in air from outside till we get higher pressure and then use some valves to "replace" the breathed up air with the fresh one
use some pressure tanks loaded with oxygen + some cleaning devices to clean the air and add oxygen to keep the same oxygen level - but this would need to get the oxygen before take-off and such tanks would be really dangerous

So how is it in reality?

The ratio of oxygen is constant.  It's only because the partial pressure is reduced that you find it difficult to breath.  Airliner hulls are far from sealed.  There are many inlets and outlets to condition air and to manage the pressure altitude.  Those movies you see where someone shoots a bullet through the fuselage leading to explosive decompression are nonsense.  You could put a fist sized hole in the fuselage and apart from noise and being able to see it, you would hardly notice.

Think of the cabin as a balloon with air coming in from some source (ex. bleed air) and with a controlled leak (outflow valve).  By adding and venting air You control the pressurize of the cabin to maintain the air pressure found at a certain altitude.  This gives you same amount of oxygen (partial pressure O2) as found as if you were walking at that altitude.

Details on how the A/C works: Why is air mixed with bypass air on the A/C of an aircraft?

They bleed hot compressed air from inside the jet engines, cool it down and pass it into the cabin. There are outlet valves in the fuselage that allow stale air out and which control cabin pressure and air-refresh rates.
A few aircraft types, such as the 787, now use a compressor to take in air from under the aircraft. They do this because it can be more fuel-efficient (not for any other reason). It is arguable whether it creates an additional fire hazard.
See also

Why is the compressed air (from Engine Compressors) taken from High Pressure (HP) stage instead of Low Pressure (LP) stage
Can an aircraft re-pressurize at high altitude?
Is constant air pressure maintained inside the fuselage?

Airplanes basically draw in outside air, compress it, and send it to the cabin. RedGrittyBrick lists some related questions about this process. Most airplanes use bleed air from the engines, using the compressors in the engines to do the compressing. Although in normal operation this will only bring in outside air, engine issues can cause fumes to enter the cabin. The 787 uses an electric compressor that draws from separate intakes.
The problem with breathing at high altitudes is not necessarily the lack of oxygen, but the low pressure. Humans need a certain partial pressure of oxygen for the lungs to work properly, and as pressures drop, the oxygen is less effective at getting into the bloodstream, which results in hypoxia. So keeping the cabin pressurized is what allows the occupants to breathe normally.
For more information about the cabin environment, see this paper. Ventilation can be expressed in "outside air changes/hour", or how often the total volume of air is replaced by new air. Airplanes have 10-15 changes/hour (every 4-6 minutes), which is 2-3 times more changes/hour than hospital delivery and operating rooms, and 4-15 times more than a typical building. New air is constantly being circulated into the cabin, while old air escapes through relief valves.

Bleed air from the engine is used to power a Pneumatic Air Cycle Kit (PACK) which takes in outside air heats it and compresses it.
The mechanism is entirely mechanical using turbines and heat exchangers and engine bleed air is isolated from the air destined to the cabin to avoid oils and fumes entering the cabin.
The answer to How hot would pressurized air get if the air conditioning failed? ex^plained in detail how a PACK works.

Do they heat or cool the air? We had this before ... see RedGrittyBrick's answer for comparison.

Reading the linked article I don't get impression bleed air is isolated from the air destined to the cabin. In fact it says the exact opposite. The bleed air is destined to cabin (a mix of cooled and non-cooled streams to achieve desired temperature) and outside air is only used as coolant.


text:
Is it possible to get access to flight logs of USAAC trainer planes from the 1930s?
After answering this question on History.SE, I started to wonder if it would be possible to find out even more detail about the plane now that its serial number is known.
I have no idea what kind of flight records the US Army Air Corps kept, however. I know most flight logs today are kept by pilot, but I imagine there would be some way to trace what pilots flew a particular plane. I have no idea if this is possible for USAAC trainer planes in the 1930s.
Could I get access to these records? If so, how would I go about it?
I'm mostly interested in seeing if I can find out more information about where the plane flew, and maybe (if I'm lucky) who flew it when and for what purpose.

For serial number 31-35
 - Pilot seems to be Brookley, Wendell H
 - Homebase seems to have been Wright Field, Dayton, OH
See Link
For serial number 31-85
 - Pilot seems to be Larkin, James D.
 - Homebase seems to have been Boeing Field, Seattle, WA
See Link
It seems that you can order any of these Reports.


text:
What would it take to pressurize a cabin with surface pressure?
At cruise level around 10000 meters the cabin pressure is lower than surface pressure. The only reason for this, is to reduce stress on the structure of the plane, or fuselage, right?
My question is this:
Given the current state of technology, if manufacturers were to produce passenger aircraft, massive or robust enough to allow cruise flight with cabin pressure equal to surface pressure, then how much would the gross weight of the aircraft increase? How much would the range of the aircraft decrease or how much less cargo could it carry?
I suppose that the current planes could also fly at surface pressure, but the level of safety would decrease, due to increased forces on the structure. So, the question really is: Suppose we want to fly at ground pressure with the same levels of safety, how much would the gross weight increase, how much less cargo could a plane carry?
Many thanks.

Are you asking how much more the structure of the aircraft would have to weigh in order to contain the additional pressure? Or how much the additional air within the cabin would weigh? Or both?

My question is fairly broad, so the answer to your question is 'both'. The engineers have a reason, why pressure in the cabin at cruise flight is rather low. I want to know, how much tickets would be more expensive with a ground pressure cabin. The children often cry in the cabin. Probably also because of the noise of the engines. But also due to the pressure.

Related: http://aviation.stackexchange.com/questions/17294/can-an-airliner-provide-ground-level-cabin-pressure-temperature-humidity-etc and http://aviation.stackexchange.com/questions/29096/has-the-typical-cabin-pressure-in-airliners-changed-in-recent-decades and http://aviation.stackexchange.com/questions/1728/does-the-b787-dreamliner-operate-with-higher-cabin-pressure

The pressure is kept lower not because the aircraft couldn't handle it, but because it would not be able to handle it for as long a lifetime. Metal fatigue and wear is dangerous as well as costs ineffective, so minimising it is a big engineering goal.

Right, Nij. Agree. And my question is this: What are the negative side effects of building more robust airplanes that would survive as well with ground pressure in the cabin as our present planes with the 2000 Meters pressure.

Related: For relationship between pressure differential and fuselage weight, see §4 in Component Weights

The SyberJet SJ30 business jet claims to offer a sea level pressure cabin through FL410 and and 1800 foot pressure cabin at its FL490 ceiling. This required extra weight, but was done for passenger comfort, reducing fatigue on long flights. They don't actually know how much weight was required, as the plane was originally designed for that cabin pressure. But it doesn't seem to have harmed performance significantly.

Not much. The current requirement for 8,000 ft equivalent pressure translates into 8.11 psi at 43,000 ft. Boeing studied the benefits of lower pressure and found that going below 6,000 ft equivalent pressure brought no additional benefits.
The full pressure differential between sea level and 43,000 ft is 12.3 psi or just 52% more than that at 8,000 ft. This would require a heavier fuselage, but would not be impossible to do at all. Statistical methods give a mass factor for the fuselage pressure differential of $(1 + ∆p)^{0.203}$ which yields 1.0933 for 8.11 psi (∆p = 0.552 atm) and 1.1314 for 12.3 psi (∆p = 0.837 atm). Increasing the pressure to its sea level value would increase the mass of a typical airliner fuselage by 3.5%.
If we use the volume of the cabin, we can also calculate how much heavier the air is: The A330-200 has a cabin volume of 372 m³, and with the density of air at 8,000 ft of 0.9633 kg/m³, this computes to 358.35 kg. Compared to the mass of the same volume at sea level (455.7 kg), the difference is roughly equivalent to the mass of a single passenger (not counting the amenities carried along for her/him, too). In other words: The added mass of air for sea level pressure will make no difference if one passenger more misses her/his flight that day.

@ymb1: It's not on the site but in the handbook, in the mass volume. I have not found an online source which lists this equation.


text:
Why no safety measures for air passengers?
Why have parachutes not been provided/safety measures taken in passenger carrying aircraft in case of a crash, so that at least they have some chance of survival?
It's like you are stuck in a bottle but until now, I am looking for an answer for how to save peoples' lives?
Even our cars have airbags in case of an accident but why nothing for air passengers?
Why is it not possible?

Hi.  Welcome to Aviation.SE. Your question is not clear.  The title asks "why no safety measures" but there are many safety measures.  Then the question asks about parachutes and air bags.  Exactly what are you trying to ask?

By safety measures i mean for example in emergencies; in cruises we have life boats, in cars we have airbags etc but in case of aircraft why shoudn't we have such thing. In case of crash u r just setting and waiting for death why not atleast try to save urself through  parachute?

There are all kinds of safety measures. Off the top of my head we have: seatbelts, seats that are tested to maintain their integrity under large amounts of force, emergency evacuation slides and rafts, emergency lighting, oxygen masks, cabin crew with emergency training, fire detection and suppression equipment, pre-flight checks, redundant systems for critical components, flight testing, an expansive regulatory regime, maintenance and inspection standards, directives to address risks, initial and recurring crew training in addressing emergencies, and crash fire rescue stationed at airports.

In any case, part of your question can be answered at Why are commercial flights not equipped with parachutes for the passengers?

see the plethora of similar questions and rants. And keep in mind that most active measures (like parachutes...) require a level of proficiency and training for the user to have any benefit from them, to the point where in many cases an untrained person (like a passenger...) would be likely to be harmed by the tool rather than it preventing harm to him.


text:
When are black boxes used?
Obviously, black boxes gather lots of media attention after tragic accidents where planes crash or explode mid-flight, since they could be crucial understanding the crash.
However, these are rather uncommon events.
Surely the black box could be used for other purposes like:

Helping the pilots understand a small mistake/hiccup/etc. on their flight
Monitor the plane's overall health
???

How often and for what purpose is black box data used?

Many data systems that might or will be used as evidence in a legal proceeding have to be used and treated in special ways or else their legal value is compromised. This extends far beyond "black boxes", but since CVRs and FDRs are expressly designed for investigation and legal action of some sort is extremely likely in the event of a crash, the forensic integrity of the data contained in them should be designed in from the start. Even read-only access can be considered to reduce forensic integrity in some situations.

You forgot 4. PROFIT

@DanHulme which is accurate in this case !

Monitoring plane's overall health is mainly done over ACARS. This transmits any fault indications over radio so the maintenance can have appropriate spare parts ready when the plane lands. Engines also similarly transmit data to the manufacturer.

There are two recorders that are mandatory on board commercial aircraft: CVR for voice, and FDR for data. They are designed to survive an accident and include an ultrasonic beacon to facilitate locating them underwater.

(Source)
It's worth mentioning that CVR and FDR are not connected to any external data port for data export/copy/extraction, and extraction of the recorders after an accident is done exclusively by the investigating agency.
(As everybody knows for years, these recorders are orange, so there is no need for journalists to continue to call them 'black boxes' as if we were not in the secret too and may not get what they are talking about...)
Cockpit voice recorder (CVR)
The CVR is a sensitive question. Crews have accepted the recording of cockpit conversations to help understand accidents. One condition is the conversations remain private in other circumstances. So there is definitely no other allowed use of the CVR.
Flight data recorder (FDR)
Certain technical parameters, like inputs on the flight controls, must be recorded, also to help determine the cause of an accident. Most FDRs record many more parameters than mandatory. Still the FDR cannot be used in other circumstances than an investigation (see section about data privacy further down).
Using in-flight data for improvement
FDR data causes less privacy concerns than CVR conversations. Safety agencies over the world have encouraged airlines and manufacturers to set up improvement programs (quality improvement) taking into account in-flight technical parameters.

(Source)
Quality improvement initiatives include:

Flight operations quality assurance, FOQA. See FAA AC 120-82.
Flight data monitoring, FDM. See Swiss FDM booklet for crews.

FDM allows companies to:

Compare their flight standards (SOPs) and the crews' actual actions. This is a way to enforce SOPs, and detect deviations from SOPs, hence crews may be reluctant to see this becoming mandatory.
Detect excessive forces applied to the aircraft, that require maintenance checks and/or repairs.
Set fuel consumption improvement actions.

As the FDR data cannot be exported, new recorders used for data monitoring and analysis are now seen on aircraft.
Quick access recorders (QAR)
Quick access recorders (QAR) are used in place of FDR, they allow much freedom, they don't have the same use and disclosure restrictions, don't have to resist a crash and can be included in wireless networks. For example this is Wifi/Ethernet QAR:

(Source)
QAR use the same data acquisition unit (DFDAU) as the FDR, using ARINC 573/717 links. They are essentially duplicating and extending the mandatory FDR, but data can be read at any time using data links. This access is not limited to investigation purposes.
Optical quick access recorders (OQAR) are QARs storing data on optical disks (e.g. Curtis-Wright), and they can record up to weeks or months of flight data. On the other hand, very small "micro" QARs exist too. This well known one uses a CompactFlash card:

(Source)
Countries like India have mandated flight data monitoring and analysis using such devices, but most regulation bodies have taken into account the reluctance of crews regarding the spreading of sensitive data, and the programs remain subject to airline decision.

Privacy aspects of CVR and FDR data
This section is likely very incomplete as the topic is complex.
ICAO:

Investigation-related recommendations are described in Annex 13 to the Chicago Convention on International Civil Aviation: Aircraft Accident and Incident Investigation.

Non-disclosure of records. 5.12 The State conducting the investigation [...] shall not make the following records available for purposes other than accident or incident investigation, unless the appropriate authority for the administration of justice in that State [...]: [...] b) all communications between persons having been involved in the operation of the aircraft; [...] d) cockpit voice recordings and transcripts from such recordings; 5.12.1 These records shall be included in the final report [...] only when pertinent to the analysis of the accident or incident. Parts of the records not relevant to the analysis shall not be disclosed.

Flight recorder cover both voice and data:

Flight recorder. Any type of recorder installed in the aircraft for the purpose of complementing accident/incident investigation.

However only CVR is mentioned in the article above, so there is some ambiguity about using FDR data.
The point about privacy is that if the information is disclosed, then the safety agencies may not be trusted in the future, information may not be provided, and security may suffer from this lack of information.

CVR in the US:

A CVR committee usually consisting of members from the NTSB, FAA, operator of the aircraft, manufacturer of the airplane, manufacturer of the engines, and the pilots union, is formed to listen to the recording. This committee creates a written transcript of the CVR audio to be used during the investigation.

(Source)

Congress has required that the Safety Board not release any part of a CVR audio recording.

(Source: ibid.).
Read also: "Privileged communications?" The bright line rule in the use of cockpit voice recorder tapes.

Recordings in EU:

Article 14, Protection  of  sensitive  safety  information in 996/2010:

the following records shall not be made available or used for purposes other than safety investigation, or other purposes aiming at the improvement of aviation  safety: (a) all communications between persons having been involved in  the  operation  of  the  aircraft; [...]. Flight data recorder recordings shall not be made available or used for purposes other than those of the safety investigation, airworthiness or maintenance purposes, except when such records are de-identified or disclosed under secure procedures.

The article above covers both CVR and FDR, but seems less restrictive than the ICAO.

Article 34 in 76/2014:

In order  to ensure the confidence of employees or contracted personnel in the occurrence reporting system of the organisation, the information contained in occurrence reports should be protected appropriately and should not be used for purposes other than maintaining or improving aviation safety.

Reading the many CVR transcripts available online, it's obvious that this rule has sometimes been transgressed. Authorities have now difficulties when making the proposition to increase the legal duration of the recordings from 2 to 24 hours.

You indicate that the CVR & FDR data cannot be used except in an accident/incident investigation. Is that specific to certain country's regulations, or is that an ICAO standard that all countries have accepted?

excellent!  I'd give you another +1 for the update, if I could.

@FreeMan Simply from an Engineering perspective its obvious. When designing a box which can survive 3400g and deep sea immersion, adding a USB port will add considerable cost to each unit. Assuming of course the device is even accessible. Not to mention it would undoubtedly reduce the robustness of the device.

@Aron: The use of FDR is not clear. This Airbus document seems to say that FDR cannot be used outside investigations, but this IATA one is less clear. There are FDR data extractors.

I believe aircraft operators are required to regularly read FDR data as part of the operational checks mandated by the regulatory authorities to ensure the FDR is functioning. They have to use this to check that recorded sensor values are correct. This suggests they have the technical means to read FDR data for other purposes.

@Aron - just because something doesn't have a USB port doesn't mean data can't be extracted from it on a somewhat regular basis. I asked mins to clarify his statement that the data cannot be used except in an incident investigation, and he did so quite admirably. A USB port, or lack thereof, has nothing to do with the regulations around when data can be used from a data collection device.

"there is no need for journalists to continue to call them 'black boxes' " Black is not a reference to their color. The name is used because they are write-only storage, only accessible to investigators. I.e. the user has no idea what goes on inside them.

@Hobbes: That's one of the usual explanations, but in engineering lingo, a black box is not so reductive. I believe we don't use 'recorder' to name a recorder as safety agencies do, mostly because they have been presented to the public as 'black boxes' by media since the beginning, media love the mystery in the phrase, "the black boxes have talked!"

I wonder why the crews opinion matters so much. After all, they're just employees of the airlines and have to follow the instructions, no matter what they think of them...

@JonathanReez: "they're just employees of the airlines", they are employees but also citizen. While an employment contract rules the employee, civil law rules the citizen, in many countries civil law includes the right to privacy as long as it doesn't cause harm to others (this is indeed a matter of balancing individual and common interests). I don't see any problem in this.

@mins I agree with the right to privacy, but the following paragraph seems weird: "This is a way to enforce SOPs, and detect deviations from SOPs, hence crews may be reluctant to see this becoming mandatory." Enforcing SOPs doesn't seem to be related to "privacy".

@JonathanReez There are understandably reasons why any employee would not want to work in an environment where their every action on the job is automatically monitored, checked against standards, and can be used for employee discipline, especially if the data may be inaccurate. At the same time, there are strong safety reasons to collect and analyze flight data. Pilots unions naturally seek to represent their members to balance that.

@JonathanReez: The problem is behavior faults that can be tracked easily can also be irrelevant regarding overall safety. If cars were monitored for speed permanently, and the authorities cancelled licenses after a very generous 50 speed limit excesses, how long would it take for the mean respectful driver to be punished? A month? Or if not punished, what would be the response of victims associations? If we open this door, it's likely we hugely increase stress and the number of accidents. This is a real question as technology now allows for such tracking to be done.

Addressing just your first item, the purpose of the cockpit voice recorder is to provide a record of all sounds in the cockpit from the time the recording stops back to however long the recording loop goes for. It should be used for accident or incident investigation only. You don't want pilots modifying what they say (or passing notes or using hand signals) because they have to be concerned with usage of the recording for anything other than accident investigation. Pilots don't expect to crash, thus, secure in the knowledge that the CVR will not be looked at except as part of accident investigation, they are free to say what they will.
Some pilots are more paranoid than others, at least they used to be back in the 1990s. I occasionally flew with pilots who availed themselves of being able to erase the CVR after a flight. On 747-100/200 aircraft you could erase the CVR if the engines were shutdown, you were on APU or ground power, and the parking brake was set. You did it by pressing and holding a button next to the microphone on the pilots overhead console.
I'm aware of at least one third-world airline that used to use the CVR to check what pilots had been saying, not for training purposes but to find out what the attitudes of the pilots were toward the company. We were flying Hadj charters for them. One day one of our captains caught them trying to change out the CVR. He ordered the offending technician off the airplane, immediately notified our management of what had happened, and made sure every captain flying on the contract was aware of the situation. I was so angered that anyone would try that kind of crap that for the next several days if any of their people came into the cockpit, I in no uncertain terms informed them that by U.S. rules (and we were in a U.S. registered airplane having to operate under U.S. rules) the CVR was to be used for accident investigation, not for spying on pilots.

Can they be used only for accident investigation, or for incident investigation too? I believe it is the later, i.e. that investigators can (and do) come for the recorders after events like serious traffic conflicts even though all the planes landed safely, nobody was hurt and nothing damaged.

The CVR can also supply useful information in the recorded sounds in the cockpit;  alarms, voice warnings,  engine noise...

@JanHudec I don't know the answer to that, but as it's obviously safety related, it would seem reasonable to allow that.

@JanHudec: From Chicago Convention Annex 13: "5.7 Effective use shall be made of flight recorders in the investigation of an accident or an incident. The State conducting
the investigation shall arrange for the read-out of the flight recorders without delay." Chapter 5.16 ensures this applies whatever the "State of Occurrence".

When are black boxes used? / How often and for what purpose is black box data used?

Recording
Reading

Accident investigation
Operational testing

Annual
Daily

Other purposes

Used for recording data
The FDR and CVR are obviously in-use, for recording data, when the aircraft is being used to transport passengers or cargo.
Used for reading data
In the event of an accident
As we all know, after an incident, the recorders are used by the investigators to retrieve the data that has been recorded prior to and during the incident.
For operational testing
There is no point having a recorder installed if it is not working. This means that the recorder must be used for operational tests.
Annual checks
The regulatory bodies have varying rules for testing of recorders.
Here is an extract from ICAO regulations

6.10.10 Flight recorders — continued serviceability Operational
  checks and evaluations of recordings from the flight data and
  cockpit voice recorder systems shall be conducted to ensure the
  continued serviceability of the recorders.
Attachment D - 3.2 : Annual inspections should be carried out as
  follows:
    a) the read-out of the recorded data from the FDR and
       CVR should ensure that the recorder operates correctly
       for the nominal duration of the recording;
b) the analysis of the FDR should evaluate the quality of
       the recorded data to determine if the bit error rate is
       within acceptable limits and to determine the nature and
       distribution of the errors;
c) a complete flight from the FDR should be examined in
       engineering units to evaluate the validity of all recorded
       parameters. Particular attention should be given to
       parameters from sensors dedicated to the FDR. Parameters
       taken from the aircraft’s electrical bus system need not
       be checked if their serviceability can be detected by other
       aircraft systems;

The French investigation body "BEA" state

2.1.5 Information on US regulations
Regulations concerning FDRs in the United States are prescribed in FAR (Federal
  Aviation Regulations), Part 125 – “Certification and Operations of airplanes which
  have a seating capacity of 20 or more passengers or a maximum payload capacity
  of 6,000 pounds or more,” section 125.226. Aircraft operators are required to
  establish a method of readily retrieving data and to maintain documentation
  sufficient to convert recorded data into engineering units (in data frame layout
  documents). However, a single document may be established for any group of
  aircraft that are of the same type and on which the flight recorder system and its
  installation are the same.
In addition, the FAA’s HBAW (Handbook Bulletin for Airworthiness) 97-13B of 15
  December 1997 provides Principal Avionics Inspectors (PAI) with guidance
  needed to evaluate FDR maintenance programmes. In particular, PAI’s should
  check if the data frame layout documents are kept up to date and any
  modifications/retrofits to DFDR systems are documented and accounted for.
  Furthermore, it is stated that, “PAI action should include air carrier operator
  readout of each airplane’s DFDR to determine that all required parameters are
  being recorded, and to verify that each parameter is working properly.”

My emphasis.
Daily checks
It is easy to find airline checklists that specify that the FDR is to be tested (e.g. Emirates 777 Freighter, p5)
I don't know what form this test takes, perhaps there is some sort of quick self-test capability built into at least some recorders?

Other Purposes

Surely the black box could be used for other purposes?

Cockpit Voice Recorders
Note that there are regulations preventing other uses of cockpit voice recorders specifically. Federal CVR nondisclosure laws (refer to 49 United States Code (USC) Section 1114(c) – Disclosure, availability, and use of information
Flight Data Recorders
This is a subject that has been looked at in the past by academics.
FLIGHT DATA PROCESSING - TECHNIQUES TO IDENTIFY UNUSUAL EVENTS begins

Modern aircraft are capable of recording hundreds of parameters during flight. This fact not
  only facilitates the investigation of an accident or a serious incident, but also provides the
  opportunity to use the recorded data to predict future aircraft behavior. It is believed that,
  by analyzing the recorded data, one can identify precursors to hazardous behavior and develop
  procedures to mitigate the problems before they actually occur.

Instead, I believe airlines, and their partners, use ACARS transmissions, Quick-Access recorders and other methods of collecting data.